Method and apparatus for using a surgical depth instrument

ABSTRACT

A method and apparatus are provided for measuring the depth of a hole with a first edge and a second edge, comprising positioning a distal end of a first member of a measuring instrument against a first surface in which the first edge is formed. Then, positioning a distal end of a second member against a second surface in which the second edge is formed, the first member and the second member being movably connected; and finally, measuring an electronic signal that represents the distance between the first member and the second member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/376,399, filed Mar. 15, 2006, which is now issued as U.S. Pat. No.7,493,703, which is a continuation-in-part of U.S. patent applicationSer. No. 11/081,147, filed on Mar. 16, 2005, which is now issued as U.S.Pat. No. 7,165,336, the contents of both being herein incorporated byreference.

BACKGROUND

The invention relates to an instrument for determining the depth of ahole and, in particular, a depth gauge for providing a digitalmeasurement of the depth of a hole in a bone.

Many surgical procedures require surgeons to secure a device to the boneof a patient. In some procedures, the surgeon spans and secures one ormore bones, or pieces of bone, using a bone plate and screws or otherfasteners. In other procedures, the surgeon uses a screw or otherfastener without another device, for example, to secure a transplantedtendon. In many procedures, the surgeon drills a hole in the bone priorto securing the fastener to the bone. With a hole in place, the surgeoncan more easily select a fastener of the appropriate length. Selecting afastener of appropriate length can be very important. If the fastener istoo long, the fastener may protrude from the bone. Typically, the boneabuts against soft tissues that may be harmed if the fastener is toolong. Although over-drilling through a metacarpal may result only inminor damage to the fat layer within the finger, if the fastener usedafter drilling is too long, the patient may experience more seriouscomplications. For example, a fastener that protrudes may be tactilelyfelt by the patient, prevent soft tissues (such as tendons, ligaments,or muscles) from moving over the bone surface, or even pierce the skin.As a different example, complications such as paralysis may result froma fastener mounted in the pedicle portion of the human spine thatprotrudes to a point where the fastener contacts the spinal cord.

During drilling, the surgeon is typically capable of feeling when thedrill has penetrated through the bone from a drop in resistance of thedrill against the bone. Because the simple act of drilling does notprovide an exact measurement of the depth of the bone, surgeonssometimes use an analog depth gauge to measure the depth of the hole.

Analog depth gauges typically comprise a central probe member having abarb at the distal end, and a reciprocating sleeve that encircles theproximal end of the central probe member. To measure the depth of a holein a bone, the surgeon abuts the sleeve against the proximal side of thehole, and extends the probe member into the hole. After extending theprobe member beyond the distal side of the hole, the surgeon retractsthe probe member, attempting to find purchase against the distal side ofthe hole with the barb. Typically, a marker is secured to the centralprobe member and the reciprocating sleeve has a graduated scale (ininches or millimeters) along a portion of its length. The surgeon readsthe measurement of depth by examining the position along the graduatedscale indicated by the marker secured to the central probe member.

A number of problems are associated with the analog depth gauge.Components of the analog depth gauge are typically manufactured fromsurgical-grade stainless steel, with the graduated scale embossed alonga portion of the length of the reciprocating member, producing a highlyreflective surface. Under bright operating room lights, surgeons find itdifficult to see the graduated scale of millimeter-wide lengthincrements. An accurate measurement of depth using an analog depth gaugerequires the surgeon to make a close examination of the graduated scalewhile holding the analog depth gauge steady. If the barb loses itspurchase on the distal side of the hole, either the accuracy of themeasurement is decreased or the time required for surgery must beextended to permit repositioning of the barb. In surgical proceduresthat require many depth measurements, these difficulties are multiplied.

There are other problems associated with the analog depth gauge. Anaccurate reading of the graduated scale requires the eyes of the surgeonto be properly aligned with the graduated scale. Viewed from an angle,the position of the marker relative to the graduated scale may bedistorted. The eyes of the surgeon may not be properly aligned with thegraduated scale while the surgeon is standing erect. The surgeon mayhave to bend over while using the analog depth gauge to make an accuratereading because if the depth gauge is tilted in order to make thereading, the sleeve will shift relative to the probe, making themeasurement less accurate and possibly causing the barb to lose itspurchase on the distal side of the hole, resulting in the samedisadvantages mentioned above.

Accordingly, there has been a need for an improved depth gauge forsurgical procedures.

SUMMARY

The present invention provides a system and a method for faster and moreaccurate measurements of depth during surgery. In an embodiment, thesystem of the present invention comprises a probe insertable into a holein a bone with an indented hook for positioning the distal end of theprobe against a first surface of the bone, and a reciprocating memberslidably connected to the probe and positionable against a secondsurface of the bone. A sensor generates an electronic signal that varieswith the distance between the first surface and the second surface. Invarious embodiments, the sensor comprises capacitors, inductors, orboth.

The present invention provides the first electronic instrument for depthmeasurement designed for use in a surgical environment. Surgicalinstruments are sterilized to prevent infection, typically by exposureto hydrogen peroxide gas. In addition, surgical instruments need tooperate consistently, even after exposure to contaminants such as water,blood, or hard and soft tissue. The demands of the surgical environmenthave thus far posed an obstacle to the design of an electronic depthmeasuring instrument. Various embodiments of the present inventionprovide an electronic surgical depth gauge that is robust tosterilization conditions and resistant to contamination. Variousembodiments of the present invention also provide a surgical depthinstrument that is easy to handle and read, producing consistentlyaccurate measurements of depth.

A variety of electronic sensors or transducers may be employed inpracticing the present invention. In some embodiments, the presentinvention employs inductive elements because of their more robustcharacteristics in environments with solid or fluid contaminants orsterilization fluids. Inductive elements may be employed in the form ofpatterned conductive loops used in conjunction with a read head assemblyof transmission and receiving loops. As will be understood by one ofskill in the art, other sensor arrangements, preexisting or which may bedeveloped in the future, may be used with the present invention, as longas they provide a signal which accurately represents the distancebetween the distal end of a hook disposed on the end of the probe and areference surface, such as the end of a tissue guard, of the instrument.

The present invention also comprises a method for using an electronicinstrument for depth measurement. In particular, the present inventionprovides the first method for taking a measurement of depth of apassageway in bone and displaying the measurement digitally. The methodof the present invention provides for substantially improved accuracy insurgical measurements of depth, which in turn means fewer problems forsurgical patients.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, advantages, and features of the presentinvention will be apparent from the following detailed description andthe accompanying drawings, in which:

FIG. 1 shows a perspective view from above of a surgical depthinstrument in accordance with an embodiment of the present invention;

FIG. 2A shows a cross-section of a surgical depth instrument in aretracted position in accordance with an embodiment of the presentinvention;

FIG. 2A′ shows an enlarged detail of a circled portion of thecross-section shown in FIG. 2A;

FIG. 2B shows a cross-section of a surgical depth instrument in anextended position and engaged with the distal surface of a bone portionin accordance with an embodiment of the present invention;

FIG. 2B′ shows an enlarged detail of a circled portion of thecross-section shown in FIG. 2B;

FIG. 3 shows an exploded perspective view of a sealed housing inaccordance with an embodiment of the surgical depth instrument of thepresent invention;

FIG. 4 shows a perspective view from below of a surgical depthinstrument in accordance with an embodiment of the present invention;

FIG. 5 shows a cross-section view of the sealed housing and body of asurgical depth instrument in accordance with an embodiment of thepresent invention, taken at section line 5-5 of FIG. 4;

FIG. 6A shows a probe with a barb in accordance with an embodiment ofthe present invention;

FIG. 6B shows a probe with a hook in accordance with an embodiment ofthe present invention; and

FIG. 7 shows a surgical depth instrument in accordance with a secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

After drilling a hole in a bone during surgery, a surgeon will often usean instrument to measure the depth of the hole before selecting afastener. The system and method of the present invention are performedusing a surgical depth gauge with an electronic sensor and digitaldisplay, which provide an easier, faster, and more accurate means formeasuring depth during surgery. While a variety of embodiments of theinvention are shown in the attached figures, those skilled in the artwill recognize that there are other mechanical and electricalarrangements for accomplishing surgical depth measurements digitally inaccordance with the present invention. Various alternative embodiments,features and variations are therefore also described herein.

Instruments used for surgical procedures must be robust both to thesolid and liquid contaminants encountered during surgery (such as tissueand blood) and the temperatures, pressures, and fluids encounteredduring sterilization (such as hydrogen peroxide gas). The twoembodiments of the present invention shown in the attached drawingsillustrate two alternative form factors for the sterilization-proof andcontamination-proof surgical depth gauge in accordance with the presentinvention. In a first embodiment 100 shown in FIGS. 1 through 5, thesurgical depth gauge comprises a tissue guard 120, sealed housing 130,and body 140 that are robust to contamination. In addition, the firstembodiment 100 can be quickly disassembled and reassembled forsterilization. In a second embodiment 200 shown in FIG. 7, the surgicaldepth gauge comprises a fully integrated body 235, in which is sealed anelectronic sensor and displays. The second embodiment is robust torepeated contamination and sterilization without disassembly.

With a hole already drilled, a surgeon might reach for a surgical depthinstrument of the present invention as shown by the instrument 100 ofFIG. 1. The instrument 100 comprises a probe 160 with an indented hook165, and a tissue guard 120 secured to a body 140. A sealed housing 130slidably engages with a side groove 144 of the body 140 of theinstrument 100. As shown in FIG. 1, the sealed housing 130 comprises adisplay window 150, ergonomic top ridges 170, and ergonomic side grooveswith ridges 180. The present invention is adapted for use by either aleft-handed or a right-handed surgeon. The side grooves with ridges 180are concave to the side surface of the sealed housing 130, and aresymmetrically disposed on either side of the sealed housing 130.

An alternative embodiment of the form factor for the present inventionis shown in FIG. 7 as the second embodiment 200. In this alternativeembodiment, the invention comprises a substantially cylindrical formfactor. As discussed above, the second embodiment 200 comprises anintegrated body 235 that is robust to contamination and sterilizationwithout disassembly. Referring to FIG. 7, the second embodiment 200comprises an integrated body 235 with slide groove 239 and displaywindow 250 formed therein. In accordance with an embodiment, so that thesame instrument may be used by both right-handed and left-handedsurgeons, a display window 250 (and accompanying display) will beprovided on both the right and left sides of the instrument. In otherwords, with respect to FIG. 7, another display window 250 (and display)will be similarly disposed on the other side of the instrument. Thedistal end of the integrated body 235 includes a tissue guard 220. In anembodiment, the method of the present invention is practiced bypositioning the distal end of the tissue guard 220 against the proximalsurface of the bone (as shown in connection with FIGS. 2A and 2B,described below). According to an embodiment, the integrated body 235 ofthe instrument 200 may be fabricated from two substantially symmetricalpieces that may be disassembled and reassembled to facilitatesterilization. As shown in FIG. 7, the two pieces fit together along aline through the middle of the integrated body 235. In variousembodiments, the two pieces may be threaded together, or sealed togetherby an adhesive resistant to contamination and sterilization. Inaddition, as shown in FIG. 7, the second embodiment form factor 200 alsocomprises finger grooves disposed towards its bottom side.

Turning back to the first embodiment of the form factor shown byinstrument 100 in FIG. 1, the instrument 100 includes side grooves 180,which are formed in the bottom piece 139 of the sealed housing 130 (seeFIG. 3). In other embodiments, however, the side grooves 180 may beformed in both the top piece 138 and bottom piece 139, such that theside grooves extend from top to bottom symmetrically along the sides ofthe sealed housing 130. As will be appreciated by those of skill in theart, in still other embodiments, the side grooves 180 may be convex tothe side surface of the sealed housing 130, and may be formed with asurface of bumps rather than ridges, or with other surfaces that providefriction and a tactile surface, even after exposure to solid or liquidcontamination. In addition, in all of the embodiments shown in theattached drawings, the display window 150 is positioned nearer thedistal end of the instrument. As will be appreciated by those of skillin the art, the display window 150 may be positioned elsewhere on theinstrument, for example, nearer the proximal end. In addition, multipledisplay windows may be disposed at various locations on the instrument.All such features and variations are contemplated within the scope ofthe present invention.

An embodiment of the method for taking depth measurements in accordancewith the present invention begins with the surgeon holding theinstrument 100 in either a right or a left hand. FIG. 2A shows alongitudinal cross-section of the instrument 100 with the probe 160 in aretracted position, and a bone portion 10 shown also in cross-section.In accordance with an embodiment of the method of the present invention,the surgeon begins a depth measurement by locating the position of thehole in the bone portion 10. As shown in the enlarged detail of FIG.2A′, the tip of the indented hook 165 protrudes slightly beyond thedistal end 122 of the tissue guard 120, thereby permitting the surgeonto sense the position of the hole when the tip of the indented hook 165slips into the hole. In this position, the distal end 122 of the tissueguard 120 abuts against the proximal surface 30 of the bone portion 10.In an embodiment, the instrument 100 is calibrated to read zero depthwhen the catch (or the proximal end) of the hook 165 is flush with thedistal end 122 of the tissue guard 120.

In an embodiment, the method of the present invention also comprises astep wherein the surgeon extends the probe 160 into the hole 20 of thebone portion 10. FIG. 2B shows a cross-section of the instrument 100 inan extended position. FIG. 2B′ shows an enlarged detail of FIG. 2B, inwhich the indented hook 165 has purchase on the distal surface 40 of thehole 20. In the cross-sections shown in FIGS. 2B and 2B′, the distal end122 of the tissue guard 120 remains against the proximal surface 30 ofthe bone portion 10 in which a hole 20 is present. From the positionshown in FIG. 2B′, the surgeon reads a measurement of depth from anelectronic display behind the display window 150 in the compartment 134of the sealed housing 130.

As shown in FIGS. 2A′ and 2B′, the bone portion 10 is bicortical, i.e.,the bone portion 10 has a first, proximal cortical layer 12 (see FIG.2A′), a cancellous layer 14, and a second, distal cortical layer 16 (seeFIG. 2B′). It should be noted, however, that the present invention issuitable for use with bones having other structures, including solidcortical, unicortical, or cancellous bones. The present invention mayeven be used for surgical depth measurement of holes or cavities inother types of tissue.

As described above, the hole 20 may be a hole formed in the bone portion10. In using the instrument 100 to measure the distance from a proximalsurface 30 formed on the proximal cortical layer 12 to a distal surface40 formed on the distal cortical layer 16, the instrument 100 operatesso that the distance between the distal end 122 of the tissue guard 120(which abuts the proximal surface 12) and the proximal end of theindented hook 165 (which has purchase on the distal surface 16) isdetermined by an electronic sensor, generating a precise measurement ofthe distance between the proximal surface 30 and distal surface 40. Theelectronic sensor may comprise inductive or capacitive elements in aread assembly on a printed circuit board and inductive or capacitiveelements in an increment assembly on a printed circuit board within thecompartment 146 of the body 140 (see FIG. 5). More specifically, theprobe 160 of the instrument 100 is inserted into the proximal edge 22 ofthe hole 20, through the hole 20, and out from a distal edge 26 of thehole 20, such that the indented hook 165 of the probe 160 extends beyondthe distal surface 40 of the bone portion 10. Extension of the indentedhook 165 away from the body 140 is accomplished in accordance with theinstrument 100 by pressing a thumb or forefinger against the top ridges170 on the sealed housing 130. As should be clear to those of ordinaryskill in the art, if the hole 20 is a hole formed by a drill bit ofcylindrical symmetry, the proximal and distal edges 22 and 26 will beapproximately circular.

The distal end of the probe 160 is equipped with an indented hook 165 inthe instrument 100 shown in FIGS. 1, 2, 4 and 7. In other embodiments,however, the indented hook 165 may be replaced with another means fordetecting the distal surface 40. In particular, FIGS. 6A and 6B show inprofile alternative mechanical embodiments of the distal end of theprobe 160. FIG. 6A shows a barb 167 at the distal end of the probe 160.FIG. 6B shows a hook 169 at the distal end of the probe 160.

With the indented hook 165 at its distal end, the probe 160 can takepurchase on the distal surface 40 of the bone portion 10. The instrument100 is shown in this position in FIGS. 2B and 2B′. Once the indentedhook 165 has completely passed through the distal edge 26, the shaft ofthe probe 160 is shifted slightly, laterally so that the indentation inthe indented hook 165 abuts against the distal edge 26. A slightretraction of the probe 160 then permits the indented hook 165 to engage(or take purchase on) the distal surface 40 of the distal cortical layer16. Retraction of the indented hook 165 is accomplished in accordancewith the instrument 100 by squeezing the side grooves 180 with thumb andforefinger, and pulling lightly. In this manner, the proximal surface ofthe indented hook 165 and the distal end of the tissue guard 120,respectively, are positioned against the distal surface 40 and proximalsurface 30 of the bone portion 10 and, through the use of slighttension, are retained thereon. In reading the electronic display whenthe invention is maintained in this physical configuration, the surgeonis provided with an accurate measurement of the depth of the hole 20 inthe bone portion 10.

Although in the embodiment depicted in FIG. 1, the probe 160 includes amechanical securement (in the form of an indented hook 165), othermechanical and nonmechanical means for positioning the distal end of theprobe 160 against the distal surface 40 of the bone portion 10 may beused in other embodiments of the present invention. In particular,electronic sensors may be used in other embodiments to detect where thedistal surface 40 terminates. For example, an ultrasonic transducer,optical or other sensor may be used to detect where the distal surface40 terminates by measuring differential acoustic or optical reflectivityor transmissivity or other characteristics as the probe 160 traversesthe hole 20. In such embodiments, an electronic sensor may be mounted tothe distal end of the probe 160 in a configuration perpendicular to thelength of the probe 160. Alternatively, the distal end of the probe 160may include only a perforation disposed perpendicular to the length ofthe probe 160, and a conduit that provides an acoustical, optical, orelectrical connection to a sensor included in the sealed housing 130. Aswill be recognized by skilled artisans, such a conduit might be providedby a hollow probe, fiber optic, or insulated wire, respectively.Moreover, in some embodiments, a current-sensing device may be placed inelectrical connection (for example, with an insulated wire) with thedistal end of the sensor to detect a change in the resistivity orconductivity of the environment local to the distal end of the probe160.

The instrument 100 further includes a reference portion that abuts theproximal surface 30. In the embodiment of the invention shown in theattached drawings, the reference portion is provided by a tissue guard120. The tissue guard 120, as shown by way of example in FIGS. 1, 2, 4and 7, has a tapered conical shape. The tissue guard includes acylindrical hollow at its core, through which the probe 160 may extendand retract. In other embodiments, the tissue guard may take a narrower,longer, or more elongated shape to permit easier passage through tissuesdisposed between the surgeon and the proximal surface 30 of the boneportion 10. For example, in another embodiment, the tissue guard 120 maybe replaced with a simple cylindrical sleeve fitted into a conical pieceat the distal end of the body of the instrument. The tapered conicalshape of the tissue guard 120 shown in FIGS. 1, 2, 4 and 7, however, maybe desirable for minimizing mechanical stress at the joints between thetissue guard 120 and body 140.

In an embodiment, the end of the body 140 nearest the tissue guard 120has a threaded nipple (not shown in FIG. 1) of diameter larger than thediameter of the probe 160. In the instrument 100, the threaded nipple isintegrally formed with the end of the body 140. In another embodiment,the threaded nipple may be secured to the distal end of the body 140 bya mechanical device or an adhesive. In all such embodiments, the tissueguard 120 is provided with a complementary threaded surface such thatthe tissue guard 120 and body 140 are secured by threading the tissueguard 120 onto the threaded nipple of the body 140. In such embodiments,the tissue guard 120 may be formed from injection molded plastic or frommachined metal. In other embodiments, the tissue guard 120 may be formedas a single, seamless piece with the body 140.

The tissue guard 120 and probe 160 are concentrically arranged such thatthe distal end of the tissue guard 122 abuts the proximal surface 30 ofthe bone portion 10 in a manner similar to that of a bone plate orfastener head. Accordingly, the tissue guard 120 and indented hook 165cooperate such that their relative position (and, therefore, distance)provides an accurate measurement of the depth of the hole 20 such that ascrew or fastener may be selected whose length is accommodated by thehole 20.

In the embodiment of the invention provided by the instrument 100,movement of the sealed housing 130 is effective to shift the position ofthe probe 160 because the probe 160 and sealed housing 130 are attachedas shown in FIG. 3. A portion of the bottom side of the sealed housing130 is formed into a mating surface 132. The probe 160 is encircled byand secured within the portion of the bottom side of the sealed housingthat forms the mating surface 132. In an embodiment, the probe 160 isinterference press-fit into the bottom piece 139 of the sealed housing130. Also shown in FIG. 3 are the mechanical parts of the sealed housing130, including the top piece 138, bottom piece 139, and seal 136. In anembodiment, the seal 136 is an o-ring seal, which is robust to repeatedcontamination and sterilization. In addition, FIG. 3 shows the displaywindow 150, which in an embodiment of the invention, is provided by apolycarbonate lens. The compartment 134 within the sealed housing 130provides the mechanical support for the electronic sensor and display(not shown in FIG. 3). As described below, the electronics secured tothe compartment 134 within the sealed housing 130 comprise the read-headassembly of an inductive or capacitive or other sensor, a display, and apower source (such as a battery).

In the embodiment of the sealed housing 130 shown in FIG. 3, electroniccomponents (including an electronic sensor, display, and power source)are sealed inside the compartment 134 with an o-ring seal 136. Inaddition, the sealed housing 130 may be sealed with epoxy, glue, orother adhesives. In other embodiments, the sealed housing 130 may bemechanically sealed with hardware, such as screws or snaps within thecompartment 134. Although the embodiment of the sealed housing 130 shownin FIG. 3 is designed to remain sealed both during surgery andsterilization, it will be appreciated by those skilled in the art thatin an alternative embodiment, the sealed housing 130 may be designed topartially or completely disassemble for sterilization. All thesefeatures and variations are contemplated within the scope of the presentinvention.

When sealed, the embodiment of the sealed housing 130 shown in FIG. 3 iswater resistant to several atmospheres of pressure. Moreover, thematerials used to manufacture the sealed housing 130 are selected to bechemically inert to chemical contaminants or sterilization fluids, bothat room temperature and at the temperatures required for sterilizationin an autoclave. For example, the sealed housing 130 may be molded fromacrylic, polyester, PVC, or other chemically inert plastic material. Inother embodiments, the sealed housing may be made from metals, such asaluminum, brass, or stainless steel. The sealed housing 130 is alsodesigned to provide only soft, rounded edges that are safe for use in asurgical environment. For example, the embodiment of the sealed housing130 shown in FIGS. 1 through 5 is in substantial compliance with theUnderwriters Laboratories sharpness test UL 1349.

Although the instrument 100 shown in the attached drawings includes adisplay, it will be understood by those of skill in the electronic artsthat the present invention may be practiced using an external display incommunication with a wireless device. In the instrument 100, a wirelesstransmitter may be connected to the read-head assembly within the sealedhousing 130. In such wireless embodiments, a wireless receiver would bepositioned a short distance away from the surgical depth gauge (forexample, on a platform near the operating table), and an electronicdisplay would be connected to the wireless receiver. In addition, as asupplement to a visual display, the instrument may be provided with anaudio readout capability that may, for example, beep or provide anotheraudible signal when the instrument senses that movement of the probe hasstopped, and there has been an appropriate interval in which to take ameasurement. In addition, the instrument may include the capability forthe distance displayed to also be audibly conveyed through a simulatedvoice from a speaker maintained within the instrument. In this manner,the surgeon's determination of the distance may also be verified fromthe audible articulation of the distance, providing further confidencein the accuracy of the reading.

A perspective view of the instrument 100 from the bottom is shown inFIG. 4. As shown in FIG. 4, the present invention includes severalergonomic features in addition to the top ridges 170 (shown in FIGS. 1and 3). In particular, the instrument 100 includes symmetrically shapedside grooves with ridges 180 and finger grooves 190. As shown in thecross-sectional end view of FIG. 5, the finger grooves 190 are formed inthe convex bottom side 192 of the body 140. In accordance with anembodiment of the method of the present invention, a surgeon would placea forefinger on a first side groove 180, a thumb on the opposing sidegroove 180, and the rest of the fingers on the finger grooves 190integrated with the body 140. The ergonomic design of the presentinvention permits a surgeon to use the system and perform the method ofthe present invention with a single hand, either right or left.Moreover, the present invention leaves the bottom side 192 entirelyunobstructed so that the surgeon is always free to grab the body 140.

Some structural features of the invention shown in FIG. 5 have theadvantage of permitting the instrument 100 to be disassembled andreassembled for sterilization. In particular, the sealed housing 130 andbody 140 are slidably connected along a mating surface 132 of the sealedhousing 130 and a reciprocal mating surface 142 formed within the sidegroove 144 of the body 140. The probe 160, which is engaged in thesealed housing 130, slides through the side grooves 144 of the body 140and into a funneled cylindrical channel formed in the tissue guard 120.In another embodiment, the tissue guard 120 may provide a keyhole-shaped(rather than a cylindrical) channel to permit probe tips withoutcylindrical symmetry (i.e., tips such as the barb 167 or hook 169 shownin FIGS. 6A and 6B) to pass through during disassembly and reassembly ofthe instrument 100. Moreover, in such other embodiments, the tissueguard 120 may be rotated after assembly to prevent the distal end of theprobe 160 from retracting within the tissue guard 120. Such a rotationis permitted when the tissue guard 120 threads onto the body 140, asdescribed above. Without a keyhole-shaped channel, probe tips ofnon-cylindrical symmetry must have a maximum width less than the totaldiameter of the cylindrical channel in the tissue guard 120.

When slidably connected as shown in the instrument 100, the presentinvention does not require oil lubricants, such that the materials areentirely compatible with a surgical environment. Referring to FIG. 3,the instrument 100 is shown in cross-section (along the plane 4-4through the sealed housing 130 shown in FIG. 3) viewed facing the distalend. The sealed housing 130 is shown in FIG. 3, with the compartment 134(again, shown without internal electronic components), and top ridges170. The seal 136 is also shown disposed between the top piece 138 andbottom piece 139 of the sealed housing 130. In addition, the matingsurface 132 of the bottom piece 139 is shown engaged with the reciprocalmating surface 142 formed by and within the side groove 144 of the body140. Also, the probe 160 is shown concentric to the end of the matingsurface 132 of the bottom piece 139. By permitting a slidable connectionbetween the sealed housing 130 and body 140, the mating surface 132 ofthe housing 130 and complementary mating surface of the body facilitatedisassembly and reassembly of the instrument 100 for sterilization.Moreover, because the surfaces are not symmetric from left to rightalong the line 5-5 in FIG. 5, the system can be reassembled only withthe display facing the distal end. The non-symmetrical design of thecomplementary mating surfaces thus prevents the present invention frombeing reassembled incorrectly.

The electronic sensors used in the system and method of the presentinvention comprise capacitive and inductive sensors and sensorassemblies. Sensors and sensor assemblies are readily availablecommercially from manufacturers such as Sylvac and Mitutoyo. Forexample, capacitive and inductive read-head and write-head assembliesare used in digital calipers, such as that made by Mitutoyo AmericaCorporation, 965 Corporate Blvd., Aurora, Ill., and by Guilin Measuringand Cutting Works, 106 Chongxin Road, Guangxi, Guilin 541002, PeoplesRepublic of China. In general, the electronic sensor secured within thecompartment 134 of the sealed housing 130 takes the form of aconventional electronic sensor, display, and power source assembly foruse in a length measuring device relying on inductive or capacitive orother elements. For some embodiments, inductive elements may provideadvantages to the extent that inductors provide more uniform andconsistent measurements through a wider variety of environmentalconditions. For example, the instrument 100 may be built with a patternof inductive loops laid down along the sensor pattern compartment 146 ofthe body 140, and a facing read-head assembly secured within thecompartment 134 of the sealed housing 130.

In various embodiments of the present invention, the electronic sensormay be connected with a microprocessor or other digital electronicdevice in order to produce an output for an electronic display, such asa liquid crystal display or light-emitting diode display. In otherembodiments, the microprocessor or other digital electronic device maybe connected to a wireless transmitter, as described above. In someembodiments, a signal conditioning circuit may interpose the inductiveor capacitive elements of the electronic sensor and the microprocessoror other digital electronic device used to drive the display, thusensuring that correct input current and voltage levels are provided tothe various components. As will be recognized by skilled artisans, apower source, such as a primary or secondary battery, may be connectedto the signal conditioning circuit or to the microprocessor directly.

The microprocessor or other digital electronic device used to drive thedisplay may be configured to provide depth measurements in inches,millimeters, or fractions thereof. In various embodiments, the sealedhousing 130 may include buttons that permit the surgeon to select howthe preferred unit of measurement is displayed. In an embodiment, themicroprocessor or other digital electronic device is configured toprovide a positive reading for depth as the probe 160 is extended fromthe proximal surface 30 toward the distal surface 40 of the bone portion10, and a zero reading when the probe 160 is retracted so that the catchof the hook is flush with the distal end of the tissue guard. In anotherembodiment, the present invention may be configured to permit are-zeroing of the device by providing a calibration button. In stillother embodiments, the present invention may provide on and off buttons(or an on/off toggling button), or a button for storing and holding themeasurement presently shown on the display for reading after the probe160 has been moved. In such embodiments, the buttons may be formed inthe sealed housing 130.

The electronic display of the present invention is selected for quickand easy visual inspection during surgery. The electronic display,however, may provide information in addition to depth measurements. Forinstance, the present invention may be provided as part of a kit (notshown) including a bone plate that mates with a head and shank formed ona screw. The electronic sensor may be calibrated to compensate for orprovide an offset corresponding to a portion of the screw head and shankreceived within the bone plate. Accordingly, the present invention couldbe configured to suggest a particular screw selected from the kit foruse with the bone plate, rather than a measurement of length. Theelectronic display may also provide an indication that the reading isnot stable, for example, because the tissue guard 120 and probe 160 arenot generally stationary relative to one another. This event is moretypical when compressible soft tissue is caught on the indented hook165, or between the tissue guard 120 and the proximal surface 30, or ingeneral when the distal end of the probe 160 is not securely positioned.In this respect, it should be noted that the probe 160 may be providedwithout any mechanical securement at its distal end. As an example, thedistal end of the probe 160 may be inserted to a depth such that itsdistal end is coincident with, but generally does not extend beyond, thedistal edge 26 of the hole 20. In using such an embodiment, the surgeonmay place a stop or finger on the distal surface 40 of the bone portion10 to stop the probe 160 when it has reached the distal edge 26.

In an embodiment, the electronic sensor and accompanying electronics canbe shielded from electromagnetic interference, for example, by coatingthe inside of the sealed housing 130 with a conductive paint containingmetal microspheres. Such shielding may be effective in reducinginterference from low frequency magnetic fields, or other strayelectromagnetic fields. Shielding is desirable at least because themethod of the present invention may be practiced in conjunction with theuse of a magnetic pad for holding surgical instruments (not shown inFIGS. 1-3).

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

A variety of embodiments of the invention are described and illustratedherein; variations of those embodiments will become apparent to those ofordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.It is not the intent of the inventors to surrender or otherwise dedicateany valid claim to the subject matter described herein to the public,and the following claims are intended to capture the entire scope of theinvention herein described.

1. A method for measuring the depth of a hole with a first edge and asecond edge, the method comprising the steps of: positioning by hand adistal end of a first member of a measuring instrument against a firstsurface in which the first edge is formed; positioning by hand a distalend of a second member against a second surface in which the second edgeis formed, the first member and the second member being movablyconnected; measuring an electronic signal that represents the distancebetween the first member and the second member; and producing an outputrelative to the measured electronic signal for reading by a user;wherein the second member comprises a sensor and a sealed housing, thesensor being contained within the sealed housing.
 2. The method of claim1, wherein producing the output comprises displaying the electronicsignal as a numerical measurement of distance.
 3. The method of claim 1,wherein, in the step of positioning a distal end of a first member, thedistal end of the first member comprises a portion selected from thegroup consisting of a barb, an indented hook, an optical sensor, and anelectrical characteristic sensor, an ultrasonic transducer.
 4. Themethod of claim 1, wherein, in the step of measuring, the electronicsignal changes in response to movement of a capacitor attached to thesecond member.
 5. The method of claim 1, wherein, in the step ofmeasuring, the electronic signal changes in response to movement of aninductor attached to the second member.
 6. The method of claim 1,wherein the sealed housing comprises at least two sides shapedsubstantially symmetrically to accommodate both left-handed andright-handed use.
 7. The method of claim 1, wherein the sealed housingfurther comprises a display, and wherein producing the output comprisesdisplaying the electronic signal as a numerical measurement of distance.8. The method of claim 1, further comprising: providing a tactilesurface comprising ridges or bumps on the sealed housing to ensure asolid grip after exposure to solid or liquid contamination.
 9. Themethod of claim 1, further comprising: providing a side groove of thesecond member; and moving the sealed housing along the side groove ofthe second member when positioning.
 10. The method of claim 1, furthercomprising the steps of: detaching the first member from the secondmember; and sterilizing the first member and the second member.
 11. Themethod of claim 1, further comprising the steps of: wirelesslytransmitting the electronic signal; and wirelessly receiving theelectronic signal by a receiver comprising a display.
 12. The method ofclaim 1, wherein producing the output comprises displaying theelectronic signal as a numerical measurement of distance on twoseparated displays located on opposite sides of a housing.
 13. A methodfor measuring the depth of a hole with a first edge and a second edge,the method comprising the steps of: positioning by hand a distal end ofa first member of a measuring instrument against a first surface inwhich the first edge is formed; positioning by hand a distal end of asecond member against a second surface in which the second edge isformed, the first member and the second member being movably connected;measuring an electronic signal that represents the distance between thefirst member and the second member; and producing an output relative tothe measured electronic signal for reading by a user; wherein, in thestep of positioning a distal end of a first member, the distal end ofthe first member comprises a portion that is an optical sensor; themethod further comprising: detecting where a distal surface terminatesby measuring a differential of an optical reflectivity or transmissivityof surrounding tissue at the distal end.
 14. A method for measuring thedepth of a hole with a first edge and a second edge, the methodcomprising the steps of: positioning by hand a distal end of a firstmember of a measuring instrument against a first surface in which thefirst edge is formed; positioning by hand a distal end of a secondmember against a second surface in which the second edge is formed, thefirst member and the second member being movably connected; measuring anelectronic signal that represents the distance between the first memberand the second member; and producing an output relative to the measuredelectronic signal for reading by a user; wherein, in the step ofpositioning a distal end of a first member, the distal end of the firstmember comprises a portion that is an ultrasonic transducer; the methodfurther comprising: detecting where a distal surface terminates bymeasuring a differential of an acoustic reflectivity or transmissivityof surrounding tissue at the distal end.
 15. A method for measuring thedepth of a hole with a first edge and a second edge, the methodcomprising the steps of: positioning by hand a distal end of a firstmember of a measuring instrument against a first surface in which thefirst edge is formed; positioning by hand a distal end of a secondmember against a second surface in which the second edge is formed, thefirst member and the second member being movably connected; measuring anelectronic signal that represents the distance between the first memberand the second member; and producing an output relative to the measuredelectronic signal for reading by a user; wherein, in the step ofpositioning a distal end of a first member, the distal end of the firstmember comprises a portion that is an electrical characteristic sensor;the method further comprising: detecting where a distal surfaceterminates by measuring a differential of an electrical characteristicincluding resistivity of surrounding tissue at the distal end.
 16. Amethod for measuring the depth of a hole with a first edge and a secondedge, the method comprising the steps of: positioning by hand a distalend of a first member of a measuring instrument against a first surfacein which the first edge is formed; positioning by hand a distal end of asecond member against a second surface in which the second edge isformed, the first member and the second member being movably connected;measuring an electronic signal that represents the distance between thefirst member and the second member; and producing an output relative tothe measured electronic signal for reading by a user; wherein the secondmember comprises a sensor and a sealed housing, the sensor beingcontained within the sealed housing; the method further comprising:coating an inside of the sealed housing with a conductive paint therebyshielding electronics and connectors located within the housing.
 17. Aninstrument for measuring the depth of a hole with a first edge and asecond edge, the instrument comprising: a first member insertable in thehole, the first member comprising a portion positionable against a firstsurface in which the first edge of the hole is formed; a second membercoaxial with the first member, the second member comprising a portionpositionable against a second surface in which the second edge of thehole is formed and a sensor that generates an electronic signal thatvaries in relation to a distance between the first member and the secondmember; and a user interface coupled with the second member, the userinterface including a housing, a display on a surface of the housingthat displays an indicia relative to the electronic signal; wherein thesecond member comprises a sensor and a sealed housing, the sensor beingcontained within the sealed housing.
 18. The instrument of claim 17,further comprising a second display on a second surface of the housingthat is opposite to the surface having the display, at least one of thedisplay and the second display displaying an indicia relative to theelectronic signal.
 19. The instrument of claim 17 wherein the portion ofthe first member positionable against the first surface is selected fromthe group consisting of a barb, a hook, an indented hook, an opticalsensor, and an ultrasonic transducer.
 20. The instrument of claim 17wherein the sensor of the second member comprises an element selectedfrom the group consisting of a capacitor and an inductor.
 21. Theinstrument of claim 17 wherein the first and second displays areelectronic displays for displaying information representative of thedistance measured by the sensor.
 22. The instrument of claim 17 whereinthe sensor of the second member is contained within a sealed housing.23. The instrument of claim 22 wherein the sealed housing comprises atleast two sides shaped substantially symmetrically to accommodate bothleft-handed and right-handed use.
 24. The instrument of claim 17 whereinthe first member further comprises a mating surface and the secondmember further comprises a complementary mating surface slidably engagedwith the mating surface of the first member.
 25. The instrument of claim17 wherein the first member and the second member are slidablydetachable to facilitate sterilization.
 26. The instrument of claim 17wherein the portion of the second member positionable against the secondsurface comprises a tissue guard.
 27. The instrument of claim 17 whereinthe sensor is connected to a wireless transmitter.
 28. An instrument formeasuring the depth of a hole with a first edge and a second edge, theinstrument comprising: a first member insertable in the hole, the firstmember comprising a portion positionable against a first surface inwhich the first edge of the hole is formed; a second member coaxial withthe first member, the second member comprising a portion positionableagainst a second surface in which the second edge of the hole is formedand a sensor that generates an electronic signal that varies in relationto a distance between the first member and the second member; a wirelesstransmitter associated with the second member having an output thattransmits information related to the generated electronic signal; and awireless receiver that is positioned away from the second member andreceives the transmitted information, the wireless receiver comprising adisplay for providing measurement data to a user of the instrument; thesecond member comprises a sensor and a sealed housing, the sensor beingcontained within the sealed housing.
 29. The instrument of claim 28,further comprising: an audio output that receives information related tothe generated electronic signal and transforms the signal into an audiosignal related to the distance between the first member and the secondmember.
 30. The instrument of claim 29, wherein the audio signalcomprises a beep.
 31. The instrument of claim 30, wherein the audiosignal comprises a simulated voice that conveys the distance between thefirst and second members.